Plant Antioxidants and Mechanisms of Action

Background: Free radicals are unstable molecules with one or more unpaired electrons that can associate and oxidize the biological macromolecules causing damage. The human organism is endowed with antioxidant defenses; however, an imbalance between these defenses and the oxidative stress, derived from excess of free radicals, can trigger the development of diseases. The fighting against free radicals can receive the reinforcement of endogenous and exogenous antioxidant molecules. Plants constitute a valuable source of antioxidant compounds, thus, this review explains the activity of the main enzymatic and non-enzymatic antioxidants of plants functioning as exogenous antioxidants for humans. Methods: Works were searched through electronic databases according to article titles, abstract text, and relevance in the field of plant antioxidant compounds. Articles were analyzed and selected by the authors (WFO and PMSS) and were approved by the other authors (LCBBC and MTSC). Results: Some pathological conditions can be initiated or exacerbated by free radicals that cause cellular and molecular damages. Plants can produce constitutively antioxidant molecules, with enzymatic or non-enzymatic action; and such synthesis can be increased in certain situations when the plants are exposed to some stressors. These compounds with antioxidant action can be identified in plant extracts and even be purified with elucidation of their chemical structure. Different in vitro methodologies can be useful for screening the antioxidant action of these molecules, for example, by evaluating the reducing power of such compounds on commercially available free radicals. Nanotechnology can be used to promote local delivery of antioxidant molecules, for example, by loading such compounds into nanotubes or encapsulating them in nanoemulsions. Conclusion: Some isolated compounds approached can be used for the design of new drugs. In addition, this article reports new nanotechnological systems that promote the delivery of plant antioxidant molecules, becoming a future perspective for the elaboration of more effective formulations with these compounds.